Belgian prosecutors said four people arrested Friday on suspicion of participating in terrorist activities have been charged in connection with a scheme to recruit jihadist fighters for service in Syria.

Authorities said the suspects were caught in a sweep of 22 locations in Limburg province, near the Dutch border. The Belgian newspaper Le Soir said no weapons or explosives were found during the arrests.

Belgium has been on high alert since January 15, when authorities smashed a terror cell allegedly plotting attacks targeting police.

In a separate development, a leader of the Yemen-based al-Qaida affiliate was quoted Friday as saying France had surpassed the United States as the top enemy of Islam.

In an audio message posted on Facebook, a voice identified as that of Ibrahim al-Rubaish singled out France, saying Muslims should attack — without consulting anyone — those who mock the Muslim Prophet Muhammad.

The French news agency AFP said the tape linked the shift toward France to a "weakening" of the United States in recent years. The tape did not elaborate.